The study, by the National Energy Technology Laboratory in Pittsburgh, is still ongoing. It’s the first time a drilling company has let government scientists inject tracers into the fracking fluid to monitor whether it spread toward drinking water sources, the AP reports.

After a year of monitoring, researchers have found the chemical-laced fluids remained about a mile below drinking water supplies.

The study is being conducted at a drilling site in Greene County, southwest of Pittsburgh and adjacent to West Virginia.

A Duke University study of wells near shale gas drilling sites in Fayetteville, Ark., published in May found no groundwater contamination. Low levels of methane found in samples were mostly from biological activity inside shallow aquifers, not from shale gas production contamination, scientists concluded.

As companies are feeling the pressure to cut their freshwater use in dry areas of the US — and they’re looking to reduce the high costs of hauling millions of barrels of water to oil and gas wells and later to underground disposal wells — an increasing number are using recycled water in fracking operations.

Also last week, Nuverra Environmental Solutions entered into an agreement with Halliburton to advance the treatment and recycling of produced water to be re-used in the fracking process. Nuverra will work with Halliburton in the Bakken Shale to utilize the Halliburton’s H20 Forward service for water re-use and recycling in fracking operations, which allows customers to recycle waste streams of produced water for use in well completions.